


Benefits

by orphan_account



Category: Life with Derek
Genre: Alternate Universe - Canon Divergence, Explicit Sexual Content, F/M, Friends With Benefits, Step-Sibling Incest, Vaginal Fingering, Vaginal Sex
Language: English
Status: In-Progress
Published: 2016-09-07
Updated: 2016-09-07
Packaged: 2018-08-13 18:43:39
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 5,022
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7982110
Author URL: https://archiveofourown.org/users/orphan_account/pseuds/orphan_account
Summary: <blockquote class="userstuff">
              <p>When Casey allows teenage curiosity and Derek's scathing remarks get to her, the end results is something she never saw coming. But as she and Derek grow closer, can they really keep up their charade of indifference? Or will their budding feelings make this casual relationship anything but casual? First published April 15th, 2009.</p>
            </blockquote>





	Benefits

**Author's Note:**

> So I wanted to talk about this before we got into the fic. This is something I wrote back in 2009 on one of my FFN.net profiles. I recently rediscovered it and decided to publish it on here. What started as some simple edits turned into a 5,000+ word rewrite. The elements are still there but it will be a little different now that my writing has grown. I also wanted to say that this takes place between Season 2 and Season 3. Everything from Seasons 1 and 2 is canon, but Season 3 and on is not. 
> 
> Thanks for reading! Feedback and kudos are appreciated.

Casey chewed on her bottom lip as she racked her brain for a comeback to Derek's latest insult. She bit her bottom lip, deep in thought. "Well at least I  _have_  a brain!" she countered at last, smirking victoriously.

Derek put a hand to his chest and stumbled back with an exaggerated stagger, teasing her even more. “I am so wounded. How will I ever recover?”

Casey rolled her eyes and huffed, crossing her arms over her chest. She tried to think of another quip to throw his way, but it was a challenge. Nothing she said ever seemed to have the profound effect she wanted it to have on him. He was so apathetic to her insults by this point that it was almost useless to say something witty to challenge him. He would simply shrug it off and come back with something that was actually hurtful.

“Don’t you ever get tired of being such a stupid jerk all of the time? Is it really that exhausting on your pea-sized brain to think of something nice to say to anyone?” she asked, her voiced filled with its usual annoyance and exasperation that a conversation with Derek left her with. All he did was smirk and shrug.

“So you’re calling me stupid, huh?” he asked, his own arms crossing over his chest. Casey gave an affirmative nod.

“That’s exactly what I’m saying. And I’m pretty certain your GPA would back me up,” she threw back, starting to feel a little cocky from his reaction. He hummed in response and she felt the need to keep going. “I, on the other hand, could outsmart you any day of the week. That means all of your low brow insults mean nothing to me.”

Derek scoffed. "You're all book smarts, Princess," he stated, uncrossing his arms and shoving his hands into his pockets.

"What is that supposed to mean?" she asked, deeply confused by his remark.

"Sure, you can pass a test…” he said in a soft, mocking voice. He started to walk closer to her and circled around her, giving Casey her turn to scoff. He moved his lips right behind her ear until his warm, moist breath ghosted against her skin. She clenched her fists, ready to turn and punch him in the gut if he got too close.

His words continued to roll off his devilish tongue while he stood only inches away from her. “But, if you were in the real world with crime…drugs… _sex_ …” he paused, smiling wolfishly, “you’d get eaten alive.”

Casey swallowed hard at his words and his breath on her neck. She was trying her best not to show how vastly uncomfortable the whole scenario was becoming. Thinking of those things and Derek in the same wavelength was absolutely abhorrent to her. Sure, she was a little bit curious about what he meant with all of that. She told herself over and over that he was just being typical asshole Derek. It was just him trying to be intimidating and gain the upper hand. She was above all of his childish attempts to get under her skin.

"Whatever," she finished, unable to come up with something else to say. She wasn’t going to lower herself to his level. She knew he’d take that as a major victory, but she’d rather think that _she_ won for not stooping down and giving into him egging her on. If she kept telling herself that, she might even believe it.

Derek grinned brightly, confirming Casey’s suspicions. He was convinced that victory was his. He patted the girl on the shoulder with a heavy hand, making her escape from under his touch. She rubbed her arm as he turned and sprinted up the stairs. She heard his door close and she assumed he was laying on his bed with that smug, confident grin she wanted to slap off his face. He thought he was so clever…

Casey sighed and ran up the stairs as well, taking them two at a time so she could get to her room to fume. She plopped onto her bed unceremoniously and crossed her arms angrily. She probably looked like Marti when George told her bedtime was in 10 minutes. Derek just got her so frustrated that she felt like she went through years of regression just talking to him. It was like talking to a toddler sometimes.

That thought felt dirty when she considered what he had been taunting her about. He called them “street smarts.” Just the words made her sag with anger. She was smart. She had the GPA and test scores to prove it. Him implying that she wasn’t smart was enough to make her seethe with rage. She didn’t need to know how to roll a joint or slip out of handcuffs to be considered smart. She concluded that “street smarts” were an idea created by people like Derek to feel better about themselves.

Her mind started to drift to the third thing he said. _Sex_. She knew that kids at school were already starting to have sex. She also knew that Derek was definitely one of those people. He wasn’t exactly shy about his conquests or the girls that came in and out of their house like they had a revolving door. Casey, on the other hand, was almost completely dumbfounded when it came to sex. Sure, years of health class and a very long sex ed class in grade nine had taught her the mechanics and repercussions of such an act. But when it came to actually doing anything remotely sexual, she was completely at a loss. She might as well be an idiot when it came to the topic. Like Derek whenever he was in any class at school.

She was disgusted by the idea that maybe Derek was a little right. Maybe there was _something_ that she wasn’t exactly the smartest at. For once, he truly had the upper hand at something. She cringed at the thought of him knowing more that she did at any topic. She’d prided herself on being smarter, nicer, and better than him. But on this front, she knew nothing and that was absolutely horrifying for her. She could not let him know more than her on anything whatsoever.

The brunette tried to think of something she could do to remedy the situation. She wasn’t about to walk out onto the street and ask someone to have sex with her. That would not only be absurd, but also incredibly dangerous. She thought that maybe she could look on the internet for some answers. Maybe even search some of the porn sites she’d heard about. But her lack of knowledge would definitely end with her getting some sort of virus on her computer that she’d eventually have to own up to. No, she’d have to find a more reasonable and safe answer to her quandary.

Her mind searched for sensible way to learn about sex. It had to be safe for both her well-being and her reputation. She had to find someone who could teach her things and keep it completely a secret. It had to be someone who knew what they were doing. It also had to be someone who would understand her need for them to keep quiet about it. She didn’t want people finding out about Casey McDonald giving into the notion of casual sex. She reminded herself that all she needed to do was learn what she needed to and then it would be over. She’d be able to move on and find someone she really wanted to be with. There didn’t need to be any strings attached.

But who did she know that was completely okay with casual, no strings attached sex? Her brain went through all of the guys she knew at their school like a long rolodex of choices. Her mind settled on someone like it was the jackpot arrow on a crappy arcade game. _Derek_. The thought made her want to gag. How could her mind even come up with the idea that Derek should be the person she would lose her virginity to? First off, it was gross. Secondly, he would probably laugh in her face if she suggested it.

Part of her agreed completely with her thoughts. It was a stupid idea. She could think of several reasons that it was a terrible idea. She could just find someone else who would help her learn what she wanted to. The other part, a part she really hated, said that she should ask him anyway. It was the perfect set up. Neither one of them could tell anyone without fear of being labeled as disgusting and indulging in an incestuous relationship. She could imagine her mom and George’s faces if they found out. The amount of secrecy and deniability was enough to give her the final courage to stand up and go to Derek’s room.

This time she didn’t pound on his door or even give it a small knock. She barged right in and shut the door behind her. Derek looked at her with a quizzical expression, removing his headphones from their place on his ears. He looked genuinely surprised with how violently she had entered the room. He appeared more astounded and confused rather than upset by her intrusion.

"Come...in?" he dragged out, still looking at her.

She was breathing in and out rapidly, clenching her fists. She needed to keep her nerve before she chickened out. Without a word, she stood at the foot of his bed, thinking this over and over in her head. She was far too deep to turn around and leave. That would just leave him with even more questions. Casey took in one last deep breath and stared Derek directly in the eyes.

"You're right. I don’t know about whatever these street smarts are,” she admitted. He sat up in his bed and gave her the smug smile she’d imagined earlier. She fingered the hem of her shirt, finally making a choice. She had to do this if she wanted to show him that she knew about the world. She was just as smart as him in every aspect.

Derek shrugged and chuckled happily. “Well, you know how much I love to say I told you so…”

Before he could gloat too much, Casey lifted her blouse over her head. His eyes widened like saucers and she heard him clear his throat. His Adam’s apple bobbed in his throat, giving her some more confidence with what she was planning. Her skin was littered with goosebumps from the new exposure and her anticipation. There was still some fear that he would laugh in her face and kick her out of his room. She had to shove that into the back of her mind and just go for it.

“I need you to teach me. Teach me about sex,” she said, coming right out and saying it. She didn’t need to beat around the bush when it came to this. She was putting herself out to him and he could either rebuff her or understand that all she wanted was to learn.

“You have officially lost your mind, Keener,” he said, sitting up even further on the bed. His mouth was saying those words, but Casey could see how his eyes were scanning her body up and down. He was checking her out. He was a guy after all and the young girl knew she was at least slightly attractive. It was a physical reaction for him, she deducted.

"I’m telling you you’re right. Isn’t that, like, your favorite thing in the world? And, I’m offering you free, unattached sex. Another one of your favorite things," she reasoned. She could see the gears turning in his head. He knew that she was right. He didn’t have to tell anyone about this and he was getting an opportunity to have sex, something he always jumped at. There was no way he would actually turn her down.

His answer was to scoot further towards the foot of the bed. “You better not tell anyone about this. Ever. If you do, I will deny it and tell everyone that you are more of a nutcase than you already are,” he insisted, his voice rushed like he couldn’t get the words out fast enough. He appeared to still be making up his mind on the whole matter. Casey hoped she could convince him.

“You really know how to woo a girl,” she mumbled, kneeling on the bed so she was in between his legs, where his knees were bent to give him more leverage. His bed felt strange, but also as expectedly comfortable underneath her weight.

He smirked and rolled his eyes. “You come into my room practically begging me to fuck you and you’re complaining about me not seducing _you_ enough?”

Hearing him refer to them having sex as “fucking” made Casey squirm a little. Even if this was some casual affair, she didn’t like thinking about it being so dirty and vulgar. She would be losing her virginity after all. She didn’t want to think of it as a quick fuck even if she knew that was what it was for him. Wasn’t that what she wanted it to be for both of them? The whole thing was already starting to become a muddled mess of confusion in her head.

Casey shook her head and leaned forward, capturing his lips in a kiss. Her fear of him pushing her away still lingered in her brain. When he started to kiss her back, she was relieved. He was getting into it as well, his hands travelling up her arms to cradle her jaw. The kisses weren’t quite passionate yet, more light and awkward. It looked like they were both trying not to laugh as they moved their mouths together in an effort to push the encounter further and closer to where they both wanted it to go.

Their kisses started to become more serious and soon Casey was pushing Derek back onto the bed. He looked surprised by the action, but didn’t dare take his lips away from hers. Casey’s entire body was quaking with the electricity of Derek’s kisses, the hairs on her arms standing up. The chill in the air was contrasted with the warmth of her step-brother’s hands leaving her face to run down her back. His palms were warm and slightly sweaty, cradling the small of her back. She could feel the bumps and raised scars from years of reckless behavior and sports. The way they dragged over her taut skin made a shiver crawl down to the base of her spine.

Their lips pulled apart in a mutual desire for air. They looked into each other’s eyes, blue irises meeting muddy browns that almost looked green in the right light. Casey hadn’t noticed how deep and almost sexy they were. The attractive qualities about him were so much better when he wasn’t talking or pestering her relentlessly. She might even be able to admire them if she stopped thinking about who it was.

His fingertips, surprisingly soft and smooth, trailed up her back to the clasp of her bra. He used his nimble digits to undo the metal hooks with surprising expertise. Casey was impressed with how quickly he was able to get them undone. She raised her chest up from his so he could slip the garment from her shoulders and off her body. He tossed it on the floor and she didn’t even know where it went. She didn’t really care. She was too focused on how she no longer had a bra on and Derek Venturi was face to face with her breasts.  

“Derek…” she whispered, looking down at him. He looked thoroughly entranced by her chest. Casey had never considered her breasts much, but the way he looked at them made her feel a little more confident. She rolled her shoulders back to give him a better look at her rosy pink nipples and the way her breasts hung slightly lower than her liking. He didn’t seem to mind any of the flaws she saw in them.

The male’s hands found her hips and he used her distraction to flip them over so he was in charge. Derek was never one to enjoy being out of control. The way he hovered over her half naked body left her unperturbed by the change in position. She was actually interested in where he was going to take this. He was the one teaching her. He needed to be in charge if he was going to show her what she needed to know.

“Kiss me,” he whispered and Casey thought for a moment that she had misheard him. Was Derek really asking her to kiss him? She didn’t question it too much and lunged up to smash their lips together once again. Derek took the time they were kissing to unfasten the belt he was wearing. Casey gasped at the thought that this was really going to happen. Derek was taking his pants off.

Casey was unsure what she should do so she reached between their bodies. She undid the button of her own pants and shrugged them down her hips. Derek was in the midst of removing his own pants when her small cotton panties were revealed. A moan rippled from deep within his throat. They weren’t even her best pair but they were doing the trick for him. The moment she saw him in his boxers, she could see the tent hidden beneath the thin fabric. He was really liking the sight of her in her underwear then.

She reached down to the elastic of his boxers. “You’re getting hard,” she whispered like she was medically fascinated with it. Something between a laugh and a groan escaped his lips at her realization.

“Well, that’s what happens,” he said playfully, kissing her throat and then the juncture between her shoulder and neck. She swatted at his chest, making him laugh lightly, which she returned. She didn’t think she could really enjoy being around Derek for a long amount of time. Maybe this was why all of the girls at their school seemed to fawn over him.

While he was kissing her tight skin, Casey felt his hand snake between their bodies. His fingers meandered down her soft stomach to the hem of her panties. She gasped, waiting for him to do something. She was expecting him to immediately remove them. Instead, his fingers ventured lower until they were pressed against her and…

Casey moaned so loud that Derek had to clamp his free hand over her mouth to keep her quiet. No one in the house could hear what was happening in his bedroom. She whimpered into the heaviness of his palm while his expert fingers rubbed over her cloth covered clit. As she moaned and writhed, Derek gave her a look that said how proud of himself he was. Casey would have said something if his hand wasn’t over her mouth and his fingers didn’t feel so damn good.

“You have to be quiet, Case,” Derek whispered before removing his hand. She nodded, though she was still whimpering as his fingers didn’t cease their movements. Even when she’d tried to touch herself before, it never felt this good. He was so talented that she would say something if it wouldn’t give him a big head. Her moans and whimpers probably said enough though.

Derek kissed down her collarbone all the way to her breast. He wrapped his lips around her stiff nub. She could feel it hardening underneath his lips and her eyes fluttered closed. The brunette balled his sheets up in her fists until her finger nails were leaving imprints on her palms. Her back arched until her tit was flushed against his mouth. He released her nipple with a loud pop. Her bud was glistening with his spit and Casey moaned at the sight.

The male removed his fingers from between her legs and brought them up to her lips. “You’re so wet,” he whispered, running his slightly damp fingers over her bottom lip. She’d never heard or felt anything more erotic, and that included when his mouth was wrapped around her blushing nipple. She wrapped her mouth around his two fingers while nodding at his statement. He groaned at the sight, obviously finding it just as hot as she was.

His hand moved to her panties once more, but this time it was to shuck them down her legs. He pulled them slowly down her muscular legs and tossed them with her other discarded clothes. She felt so exposed, completely naked while he was still in his shirt and boxers. She took the initiative to pull his shirt over his head to even the playing field. He allowed it to happen and the moment it was off, he returned his lips to her protruding collarbone.

Derek’s knee brushed against Casey’s newly exposed center and she moaned. Her wetness, which was quite apparent now, left a small spot on his leg. He removed his fingers from her mouth, though he still dragged the soft pads against her raw bottom lip briefly. She tingled at the sensation and her toes curled in anticipation of what was to come. His wet fingers moved to her sex, dripping with wetness so much that she felt a small bead roll down from her pussy to her puckered asshole. It cooled on her skin from the air and she shivered. Derek obviously caught the sight and moaned from the sheer hotness of it.

His fingers slipped between her damp folds, sliding inside of her tight mound. Casey hadn’t felt anything inside of her other than her own fingers. Even she hadn’t made herself feel as good as Derek was. He stroked his fingers in a “come hither” type movement, making her squeal in a way she’d never heard her own voice sound. She saw stars behind her eyelids when she snapped them closed in pleasure. It was like fireworks lighting up the night sky. She never wanted to lose this feeling.

“Is…is that my…” she rasped out, not even sure what she was trying to ask. As he continued to rub and tease her, her mind was becoming a whirlwind of colors and sensations. She chewed on her lip, barely remembering the question she had asked him only moments before. What had she even been trying to say?

Derek chuckled and nodded. “Yeah. That’s it,” he whispered, kissing the valley between her breasts. He didn’t even need to say the actual word for Casey to nod and whimper with excitement. The muscles in her thighs were trembling with arousal while her stomach tightened with an impending orgasm. She chased her need to release by grinding against his hand, feeling his palm drag against her clit. She was getting so close that she almost screamed in disappointment when he withdrew his fingers.

She pouted up at him while he chuckled. He reached across her body to the drawer beside his bed. She heard it opening and then the crinkling of a wrapper. His hand returned with a rubber condom between his fingers. He quickly shed his boxers, barely giving the young girl a good look at his bare member. She watched as her step-brother rolled the item onto his hard cock, securing it properly. Casey looked up with anticipation and a bit of fear. This was really going to happen.

Just as Derek finished placing the condom on his shaft, their eyes met. He took it as a sign and reached one hand up to cup her cheek. He leaned down and placed a gentle, almost loving kiss on her lips. “I’ve got you, okay?” he whispered in the genuine tone Derek only had when he was being truly serious. Hearing him talk like that had Casey trusting him completely. She nodded and waited for what was coming next.

She felt the head of his length push against her sex before it started to slip it. It was a tight fit at first and a bit uncomfortable as she tried to adjust to his size. He pushed in slowly, but all of the way. She took him with a little bit of effort. He gave her time to get more comfortable with him inside of her. She could see the struggle in his eyes as he tried his best to stay completely still. She couldn’t imagine how he was feeling inside of her.

When she finally adjusted to him, he started to withdraw his hips and then push back it. She winced at first until he started to go in and out with less friction. Casey started to feel something when the head of his cock pressed against the sweet spot inside of her that he’d introduced her to only moments before. She gasped and thrashed on the bed. He had to use his hand to keep her down so she didn’t hurt either of them. With her easily pinned, Derek moved faster inside of her tight channel.

Casey continued to moan and whine as he thrusted into her. She was anticipating him to just pound into her, but he was being surprisingly delicate with her. He still moved inside of her with urgency and dedication; however, that didn’t keep him from making sure she was feeling as good as he was. Whenever he missed the perfect pleasure inside her, he made sure to kiss her neck or swipe his thumb over her firm nipple. He did nothing to cause her pain or discomfort. This _must_ be why the girls at school loved him so much.

The white noise pounding in her ears from the sensations and perfection of the moment was only drowned out by Derek’s throaty moans and passionate groans. His noises were the perfect finale to the symphony coursing through her veins while he pushed himself in and out of her. It was a long, drawn out moan from him that finally sent Casey tumbling over the edge. Her orgasm hit her harder than anything had. Her moan was caught in her throat as her lungs burned in need of oxygen. Her eyes rolled back as her legs clamped together and her throat finally gave way to breath. She didn’t know how long she was under the spell of her climax, but by the time she could have a coherent thought, Derek had pulled out and was tossing the used condom in the trash. So he had cum too. She hadn’t even felt it.

Once the condom was discarded, Derek rolled off of her and laid on his bed. Casey looked over at him, watching as his chest rose and fell as he tried to catch his breath. She was feeling the same way, her lungs finally inflating correctly. She had never felt something so explosive than what she had just experienced. It was like she had been consumed by true bliss. She knew what the height of pleasure was and she didn’t want to lose that feeling. The fact that she had been so nervous was replaced by her overwhelming joy. The way her nerves still lit up with the aftershocks of such an event told her she needed to do it again and again.

“Wow,” she gasped, looking over at him. Before she could add to her statement, Derek was shifting and grabbing his pants from the floor. He stood and pulled them back on with a speed she hadn’t seen him have outside of a hockey game. She sat up while he picked up her shirt and pants, throwing them on the bed beside her.

He tugged his shirt onto his body, fully clothing himself. “You need to leave,” he said. He waited for her to get up, giving her a violent gesture that said to hurry up. She scoffed and started to dress herself. She forgot that her bra and panties were still somewhere scattered on the floor. She was too focused on the way he was pushing her out. How could he just give her the greatest orgasm and then expect her to run away? Her mind screamed that this is what she wanted. Casual sex to teach her something. Nothing more; nothing less.

“Derek…” she breathed but he shook his head. The moment she was clothed, he pressed his hand against her chest. She was waiting for something else. Some sort of move or show of affection. Instead, he gave her a sharp push while using the other hand to open the door. Another push and she was out of the room. The door slammed shut the second she was out, leaving her absolutely astonished. How could he do that to her?

She turned and stomped off to her room. The second she hit her bed, she felt something like tears brimming in her eyes. How could she be so stupid? She’d learned what she wanted but at what cost? Her first time and she wasn’t even allow to soak in the afterglow. Instead, she was shoved out like any other girl who had come into that bedroom before her. She shouldn’t be surprised, but her chest ached from the gravity of the situation.

As she rolled onto her side, she clutched her chest tight. She had just lost her virginity. She had lost her virginity to _Derek_. The thought should make her gag, but instead, she smiled a weak grin. Then, she yawned despite her efforts to stay awake. The last thing she thought of before drifting into sleep wasn’t the way Derek kicked her out with nary a second thought. She remembered the way Derek had been so gentle with her. How his hands and lips felt on her body. And the way his moans rang in her ears. She couldn’t even make herself think of how disappointed she was about him pushing her out.

What did she have to be disappointed about anyway?


End file.
